Inhibition of metal corrosion



United States Patcht 2,989,485 7 INHIBITION OF METAL CORROSION Louis H. Eilers, 'Inlsa, Okla, assignor to The DowChemical Company, Midland, Mich., a corporation of 'Dela- Ware i No Drawing. Filed May 21, 1958, Ser. No. 736,704

, 9 Claims. (Cl. 252-151) The present invention relates to the inhibition of metal corrosion and more particularly relates to .a new and useful composition which prevents the corrosion of fercentrations of either oxidizing acids or non-oxidizing acids. Another object of the present invention is'to provide a corrosion inhibitor composition which will not decompose under the oxidizing conditions. It is still a further object of the present invention to provide an inhibitor which will permit the storage of nitric acid in metal containers. These and other objects will become apparent to those skilled in. the art from the following specification and claims.

It has now been foundthat acid corrosion of metals, particularly that caused by the oxidation effect of nitric acid, can be inhibited by mixing with the acid system a beta-activated mercaptan and/or a gamma-activated sulfur compound such as, for example, one or more of the sulfur compounds of .the class alkanedithiols, mercaptoalkanols, dimercaptoalkanols, 'mercaptoalkanoic, acids, or thioalkanoic acids, furfurylthiol and-the like.

Good results are obtained when the sulfur-containing inhibitor is employed in an amount of from 0.06 to 1.0 percent by volume of ultimate composition.

In accordance with the present invention, when the sulfur compound or compounds of the present invention are mixed with acid i.e., a mineral acid such a nitric, hydrochloric, sulfuric, phosphoric or perchloric acid or the lower organic acids such as acetic and the like in an amount of from 0.06 percent to 1.0 percent and preferably from 0.25 percent to about 0.5 percent by volume of the ultimate composition, the corrosion of metal surfaces in contact therewith is substantially inhibited.

Various combinations of sulfur-containing compounds may be employed to prepare the inhibitor compositions of the present invention. Thus, one or more of the following sulfur-containing compounds, i.e., ethanedithiol, 1,2- or 1,3-propanedithiol, butanedithiol, pentanedithiol, hexanedithiol, thiolacetic acid, 2,3-dimercapto-l-propanol, 1,3-dimercapto-2-propanol, furfurylmercaptan or the like may be employed.

The inhibitor of the present invention can be added to the aqueous oxidizing acid or the acid can be added to an aqueous dispersion of the inhibitor. The latter method is more often preferred since the mixing of the acid can take place in ferrous containers whereas the first method requires non-corrodible equipment prior to complete dispersion of the inhibitor in the acid solution.

The following examples are illustrative of the present invention but are not to be construed as limiting.

Examples 1-6 Corrosion rate tests employing various concentrations of 1,2-ethanedithiol as the active inhibitor in 10 percent nitric acid were made to determine the concentration of t nte -fl e? 6.

2 inhibitor composition required for adequatejprotection the results ofwhich are shown below? :-.v

Volume acid1 50 ml. 2

5 Metal-AISI 1010. mild steel coupons (2.! x 1.0" .1 0.12")

Length of test-6 hours 'llemperature-80 F.

Concentration Inhibitor (percent by volume) 1O Corrosion Rate Example N 0.

too high to measure; D0.

I Examples 7-14 Additional tests were run, varying the acid concentration and temperature to show the effectiveness of the inhibit Volume acid-150 m1.

Inhibltor0.l; percent (by volume) of Lil-ethanedithiol Metal-AISI 010 mild steel coupons (2.75" x 1.0" x 0.125

Length of test d hours i5 1&8 grooke down in 2.5 hours. -20- 150' broke-down-inihours.

80 broke down in 3.5 hours.

Examples 15-26 Volume acid-15!) ml. Metal-AISI 1010 mild steel (2.75" x 1.0 x 0.125") Conditions of test-16 hours exposure at 150 ll.

Ex. Concentration Inhibitor Corrosion No. Acid Medium (percent by volume) Rate (lbs./

itJ/day) 15.-.- 10 percent Hydrochloric- None 0. 012 16. do 0.5 2-furylmethanethioL- 0. 0021 17- do- 0.5 l,2etl1anedithiol 0.0013 18 d 0.5 1,3propanedithiol 0. 0009 19. None 0.140 20 0.5 1,2-ethanedithioL. 0. 00063 21 0.5 l,3propanedlthiol 0. 00007 0.5 iuriury thiol. 0. 0009 None l 0. 185 o 0.5 1,2-ethsnedltl1iol 0. 0082 25. 5 percent Phosph0rlc.... None 0. 080 5 26. do 0.5 LZ-ethanedithiol. 0. 00072 Examples 27-36 A series of metals was exposed to 10 percent mtnc acid with and without inhibitor to determine the effec tiveness of the inhibitor in preventing corrosion of these various metals'. L5 percent by volume of 1,2-ethanedithiolwas employed.

Yolume-acld=-.-150.ml. I LenEth'oHest B Murn Temperature-80 F. I 1

- r i 7 'CilifrOsion Ex. No. Metal Coupon filiibitor; -Rnte;(1bs.l

annoy [ti/day) volume) 10 A151 347 None 0. 0018 Ami-347. 0. 5 0. 0009 None 0. 828 0. 0. 079

None 0. 0040 .0. 5 0.0004 None 0.020 0. 5 0. 0023 None 0. 0039 0.5 0. 0029 Examples 38-41- Tests were run with. various. sulfur-containing compounds to determine the length of time the mixtures give corrosion-prot tion. .5 a a Volume acid150 ml. 10 percent nitric acid Metal-AISI 10'10 mild steel coupons Length of tests-6 hours Temperature80' If.

I claim:

1. A corrosion-inhibited aqueous nitric acid solution comprising nitric acid and; as a corrosion inhibitor therefor, about 0.125 to 1.0 percent by volume of a sulfur-containing compound selected from the group consisting ofloweralkanedithiols, furfurylthiol, lower mercaptoalkanols, lower. dimercaptoalkanols, and lower thiolalkanoic acid.

2. An aqueous acid solution as set forth in claim 1 wherein said corrosion inhibitor is employed in a concentration of from 0:25 to 0.5 percent by volume.

3. A corrosion=inhibited aqueous nitric acid solution comprising nitric acid andq from 0.125 to 1.0 percent byvolumeof 1,2-ethanedithiol. r

4. A corrosion-inhibited aqueous nitric acid solution comprising nitricacid' andfrom 0.125 to 1.0'percent by volume of 'l,3-propanedith iol.. r

5. A corrosion-inhibited aqueous nitric acid solution comprising nitric acid and from 0.125 to 1.0 percent by volume of furfurylthiol.

6. A corrosion-inhibited aqueous nitric acid solution comprising. nitric acid and. from 01125 to. 1.0 percent by volume of 1,4-butanedithiol. I

' 7; A corrosion-inhibited aqueous nitric. acid solution comprising nitric acid and from 0.125 to 1.0 percent .by volumeof 1,5-pentanedithiol.

8. A corrosion-inhibited aqueous. nitric acid solution comprising nitric acid and from 0.125t0 1.0 percent by volume of 1,6-hexanedithiol.

9. A corrosion-inhibited aqueous nitric acidsolution comprising nitric acid and from 0.125 to 1.0 percent by volume of 2,3-dimercaptopropanol.

RetrencesCitdin-the fi1e-of this patent Barnes et al. Oct. 7,1952

' UNITED STATES- PATENTOFFICE v CERTIFICATE OF CORRECTION Patent No.-2 989 485 June 20 1961 Louis .Eilers Column 3,, in the fi rst table column 2, for "010" line 9 thereof read 30031114 Aluminum Signed and sealed this 10th day nf April 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents i Pa tent NO. 2 V 989 V 485 UNITED :STATESNPATENT; OFFICE CERTIFICATE OF CORRECTION June 20 1961 Louis ,Eilers It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below. a a

Column 3 in the first table column 2 line 9 thereof for "do" read 3003Hl4 Aluminum '0 Signed and sealed this 10th day of April 1962.

(SEA L), Attest:

i ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents 

1. A CORROSION-INHIBITED AQUEOUS NITRIC ACID SOLUTION COMPRISING NITRIC ACID AND, AS A CORROSION INHIBITOR THEREFOR, ABOUT 0.125 TO 1.0 PERCENT BY VOLUME OF A SULFUR-CONTAINING COMPOUND SELECTED FROM THE GROUP CONSISTING OF LOWER ALKANEDITHIOLS, FURFURYLTHIOL, LOWER MERCAPTOALKANOLS, LOWER DIMERCAPTOALKANOLS, AND LOWER THIOLALKANOIC ACID. 